Nam-Seok Joo

Objective: Resistant starch is associated with metabolic benefits, but whether autonomic regulation links resistant starch intake to cardiovascular outcomes remains unclear. This study examined the effects of resistant starch on heart rate variability and blood pressure in women with features of metabolic syndrome. Methods: In this 8-week randomized, double-blind pilot trial, 30 women (aged ≥ 40 years) with ≥2 metabolic syndrome components were assigned to a high-resistant starch or low-resistant starch group. The primary outcome was the change in systolic blood pressure from baseline to week 8. Secondary outcomes included heart rate variability-related autonomic parameters, whereas other blood pressure and metabolic syndrome-related variables were evaluated as exploratory outcomes. Results: Systolic blood pressure decreased significantly within the high-resistant starch group (p = 0.037), although the baseline-adjusted between-group difference was not statistically significant. This change occurred without corresponding improvements in body mass index or triglyceride levels. Group-level heart rate variability differences did not reach statistical significance; however, exploratory analyses suggested a favorable directional pattern in global heart rate variability composite scores among participants with lower baseline autonomic activity (p = 0.06). Conclusions: High-resistant starch intake demonstrated exploratory signals of reduced systolic blood pressure and heart rate variability-related autonomic adaptation, particularly among participants with lower baseline autonomic activity. These findings warrant confirmation in adequately powered randomized controlled trials.

Serum vitamin D level is inversely associated with non–high-density lipoprotein/high-density lipoprotein ratio: a cross-sectional study utilizing Korea National Health and Nutrition Examination Survey 2022–2023 data

The cutoff value of serum triglyceride/high-density lipoprotein cholesterol ratio of high pericardial adipose tissue in Korean: a retrospective study

Background/Objectives: Adequate calcium and vitamin D intake, along with regular physical activity, is essential for maintaining skeletal health in postmenopausal women. In populations with low dairy consumption, sustainable and bioavailable calcium sources are required to support bone integrity. Eggshell powder offers a highly bioavailable, eco-friendly, and cost-effective calcium source consistent with environmental sustainability goals. This pilot randomized, double-blind, controlled trial investigated the effects of calcium- and vitamin D-fortified home meal replacements (HMRs) made with eggshell powder, combined with weight-bearing aerobic exercise, on bone mineral density (BMD) and bone turnover markers in postmenopausal women. Methods: Thirty-six women aged 50–59 years were randomly assigned (1:2 ratio) to a control group (regular HMR) or an intervention group (HMR fortified with 418 mg eggshell-derived calcium and 837 IU vitamin D). Participants consumed one HMR daily, five days per week, and were encouraged to engage in weight-bearing aerobic exercise for 30–60 min, five times weekly, over six months. Results: High adherence was observed for both dietary (94%) and exercise regimens. No significant differences were found between groups in overall BMD or bone metabolic markers after six months. Exploratory post hoc subgroup analysis suggested possible exercise–nutrition interactions in lumbar spine BMD. Conclusions: No significant overall BMD effect was found. Fortified HMRs achieved excellent adherence and corrected nutrient deficiencies, demonstrating feasibility. Future large-scale trials with adequate power based on realistic effect sizes are warranted to evaluate reproducibility of these exploratory findings.

Background/Objectives: Resistant starch intake has been shown to influence gut microbiota composition and affect metabolic markers. These effects may be partially attributed to enhanced short-chain fatty acid (SCFA)-mediated energy harvesting and hepatic lipogenesis induced by resistant starch fermentation. However, there is a lack of prospective research addressing these associations. To address this gap, we performed a double-blind, randomized dietary intervention study to investigate the impact of high versus low resistant starch consumption on metabolic markers and gut microbiota among adult women presenting with risk factors for metabolic syndrome. Methods: A total of 30 participants were randomly assigned to either the low-resistant starch (LRS) or high-resistant starch (HRS) diet groups. Each group, comprising 15 participants, consumed one food product per day enriched with either high or low resistant starch for 8 weeks. Changes in metabolic indices and gut microbiota were assessed and compared with baseline values, as assessed before diet (Week 0). Results: After 8 weeks of intervention, the HRS diet significantly increased body weight, body fat, and triglyceride (TG) level (mean change ≈ +40 mg/dL), while reducing blood pressure. Analysis of intestinal microbiota in the HRS group revealed a statistically significant increase in the genus Veillonella following the intervention. Conversely, the genus Marvinbryantia increased significantly in the LRS group. Conclusions: In women with metabolic risk factors, resistant starch supplementation elicited mixed metabolic responses—showing a modest reduction in blood pressure but concurrent increases in adiposity and TG concentrations. As the TG elevation reached a clinically meaningful magnitude, dietary interventions involving high-resistant starch should incorporate regular lipid monitoring to ensure cardiometabolic safety. Collectively, these findings highlight the complex interplay between SCFA-producing gut microbiota and host energy metabolism, suggesting that individualized dietary strategies may be required to optimize metabolic outcomes.

Objectives: This study aimed to investigate both the linear and non-linear associations between serum 25-hydroxyvitamin D [25(OH)D] levels and serum uric acid concentrations in Korean adults, with a particular focus on the vitamin D-insufficient range (p < 0.001). However, in multivariate regression adjusting for confounders, a weak positive association emerged. Restricted cubic spline analysis revealed significant positive associations in the lower quartiles (Q1–Q3), with the strongest association in Q3 (β = 0.769, 95% CI: 0.34–1.19, p < 0.001). No significant association was observed in the highest quartile (Q4). Conclusions: Serum vitamin D and uric acid concentrations show a non-linear relationship, with a significant positive association within the vitamin D-insufficient range (<30 ng/mL). These findings provide new insights into the potential metabolic role of vitamin D and highlight the need for longitudinal and interventional studies to clarify causality and clinical significance.

Objectives: To investigate a non-linear relationship between serum vitamin D level and uric acid concentration and to evaluate the potential of vitamin D as a biomarker for inflammatory diseases such as hyperuricemia. Methods: Using data from the Korea National Health and Nutrition Examination Survey (KNHANES), an analysis was conducted on 10,864 adults aged 19 years or more. Serum vitamin D levels were categorized into quartiles (Q1–Q4) for analysis. Their linear and non-linear relationships with uric acid concentrations were assessed using Pearson correlation analysis, analysis of variance (ANOVA), and restricted cubic spline regression. Confounding variables including age, sex, BMI, kidney function, chronic diseases, and macronutrient intake were adjusted for in the analysis. Results: In univariate analysis, a statistically significant but weak negative correlation was observed between serum vitamin D and uric acid levels (Pearson’s correlation coefficient: -0.089, < 0.001). However, after adjusting for confounders, multivariate regression revealed a weak positive association. Restricted cubic spline regression identified significant positive associations in lower quartiles (Q1–Q3), with the strongest effect observed in Q3 (beta-coefficient: 0.643, 95% CI: 0.09–1.20, p = 0.023). No significant association was found in the highest quartile (Q4). Conclusions: Vitamin D and uric acid metabolism have a non-linear relationship, particularly showing a positive association in vitamin D insufficiency (< 30 ng/mL). These findings support the potential of vitamin D as a biomarker for hyperuricemia and related inflammatory-metabolic diseases.

Calcium and vitamin D deficiencies have been ongoing problems in Koreans due to a lack of food sources of calcium and vitamin D. Postmenopausal women aged 50 to 64 years (n = 25) were randomly assigned to consume three home meal replacements (HMRs)/week with (treatment) and without (control) eggshell powder and vitamin D for 6 months. Additionally, subjects who agreed to continue the study consumed the same three HMRs/week for an additional 6 months in this randomized double-blind study. We confirmed the high compliance of the study participants by analyzing carotenoids, the bioactive substances of HMRs, in the blood. The treatment group consumed an additional 261 mg/d of calcium and 10.3 μg/d of vitamin D from the HMRs, thus meeting the recommended intakes of calcium and vitamin D for Koreans. As a result of consuming fortified HMRs for 6 months, the decline in femoral neck bone density was significantly reduced in the treatment group (p = 0.035). This study indicates that inexpensive eggshell powder may be a good source of calcium for populations with low consumption of milk and dairy products. Additionally, functional HMRs fortified with eggshell powder and vitamin D can be a good dietary strategy for bone health.

Background: Serum thyroid-stimulating hormone (TSH) levels change during body weight reduction. However, the changes that occur during short-term body weight control interventions remain controversial. Thus, this study aimed to evaluate the changes in TSH levels according to body fat reduction.Methods: We performed a 3-month intervention study involving partial meal replacement. Forty-nine participants completed the study. Correlations between changes in TSH levels and other body composition parameters were determined. The subjects were divided into two groups according to their body fat reduction (>1 kg, n=20; 1 kg, can reduce serum TSH concentrations in subjects with metabolic syndrome after short-term body weight intervention.

Identifying and preventing modifiable risk factors for cardiovascular disease is very important. Vascular calcification has been studied clinically as an asymptomatic preclinical marker of atherosclerosis and a risk factor for cardio-cerebrovascular disease. It is known that higher homocysteine levels are associated with calcified plaques and the higher the homocysteine level, the higher the prevalence and progression of vascular calcification. Homocysteine is a byproduct of methionine metabolism and is generally maintained at a physiological level. Moreover, it may increase if the patient has a genetic deficiency of metabolic enzymes, nutritional deficiencies of related cofactors (vitamins), chronic diseases, or a poor lifestyle. Homocysteine is an oxidative stress factor that can lead to calcified plaques and trigger vascular inflammation. Hyperhomocysteinemia causes endothelial dysfunction, transdifferentiation of vascular smooth muscle cells, and the induction of apoptosis. As a result of transdifferentiation and cell apoptosis, hydroxyapatite accumulates in the walls of blood vessels. Several studies have reported on the mechanisms of multiple cellular signaling pathways that cause inflammation and calcification in blood vessels. Therefore, in this review, we take a closer look at understanding the clinical consequences of hyperhomocysteinemia and apply clinical approaches to reduce its prevalence.